1. Field of the Invention
The present invention relates to an antenna system to be installed in a vehicle, such as an automobile.
2. Description of the Related Art
In a so-called hybrid vehicle where an engine and a motor are used together, or in an electric vehicle, an electronic device, such as a motor and an invertor, is installed. Since noise emitted from such an electronic device affects a radio wave in a medium frequency (MF) band or in a low frequency (LF) band, there are some cases where receiving performance of an antenna for receiving a radio wave in the MF band or in the LF band is lowered.
As a technique for addressing reception disturbance caused by noise emitted from a noise source inside a vehicle, Patent Document 1 has been known, for example. Patent Document 1 discloses a technique against reception disturbance of a broadcast signal.
Patent Document 1 discloses a technique for eliminating, for a broadcast wave antenna, noise inside a vehicle, by providing, for the antenna for receiving broadcast waves (the broadcast wave antenna) installed at a position where broadcast waves can easily reach, an antenna for detecting noise (a noise detection antenna) at a bottom portion of a vehicle body, which is a location where broadcast waves tend not to reach.    Patent Document 1: Japanese Unexamined Patent Publication No. 2013-168744
According to the technique of Patent Document 1, however, it is necessary to install the noise detection antenna at a location where broadcast waves tend not to reach, so that it is not possible to install the noise detection antenna at a location where broadcast waves reach equally as the location where the broadcast antenna is installed.
There is a need for an antenna system such that a noise detection antenna is installed at a location where broadcast waves reach equally as a location where a broadcast antenna is located, so that reception performance of a broadcast wave antenna for receiving the broadcast waves can be prevented from being lowered by noise from a noise source.